The present invention relates to protein derivatives, comprising a tumor-associated antigen, that find utility in cancer vaccine therapy. In particular the derivatives of the invention include fusion proteins comprising an antigen encoded by the family of MAGE genes (e.g. MAGE-3, MAGE-1), linked to an immunological fusion partner which provides T helper epitopes, such as, for example the lipidated form of protein D from Haemophilus influenzae B; chemically modified MAGE proteins wherein the antigen's disulphide bridges are reduced and the resulting thiols blocked and genetically modified MAGE proteins provided with an affinity tag and/or genetically modified to prevent disulphide bridge formation. Methods are also described for purifying MAGE proteins and for formulating vaccines for treating a range of cancers, including, but not limited to Melanoma, breast, bladder, lung, NSCLC, head and squamous cell carcinoma, colon carcinoma and oesophagus carcinoma.
Antigens encoded by the family of MAGE genes are predominately expressed on melanoma cells (including malignant melanoma) and some other cancers including NSCLC (non small cell lung cancer), head and neck squamous cell carcinoma, bladder transitional cell carcinoma and oesophagus carcinoma, but are not detectable on normal tissues except in the testis and the placenta (Gaugler, 1994; Weynants, 1994; Patard, 1995). MAGE-3 is expressed in 69% of melanomas (Gaugler, 1994), and can also be detected in 44% of NSCLC (Yoshimatsu 1988), 48% of head and neck squamous cell carcinoma, 34% of bladder transitional cell carcinoma 57% of oesophagus carcinoma 32% of colon cancers and 24% of breast cancers (Van Pel, 1995); Inoue, 1995 Fujie 1997; Nishimura 1997). Cancers expressing MAGE proteins are known as Mage associated tumours.
The immunogenicity of human melanoma cells has been elegantly demonstrated in experiments using mixed cultures of melanoma cells and autologous lymphocytes. These culture often generate specific cytotoxic T lymphocytes (CTLs) able to lyse exclusively the autologous melanoma cells but neither autologous fibroblasts, nor autologous EBV-transformed B lymphocytes (Knuth, 1984; Anichini, 1987). Several of the antigens recognised on autologous melanoma cells by these CTL clones are now identified, including those of the MAGE family.
The first antigen which could be defined through its recognition by specific CTLs on autologous melanoma cells is termed MZ2-E (Van den Eynde, 1989) and is encoded by the gene MAGE-1 (Van der Bruggen, 1991). CTLs directed against MZ2-E recognise and lyse MZ2-E positive melanoma cells from autologous as well as from other patients provided that these cells have the HLA.A1 allele.
The MAGE-1 gene belongs to a family of 12 closely related genes, MAGE 1, MAGE 2, MAGE 3, MAGE 4, MAGE 5, MAGE 6, MAGE 7, MAGE 8, MAGE 9, MAGE 10, MAGE 11, MAGE 12, located on chromosome X and sharing with each other 64 to 85% homology in their coding sequence (De Plaen, 1994). These are sometimes known as MAGE A1, MAGE A2, MAGE A3, MAGE A4, MAGE A5, MAGE A6, MAGE A7, MAGE A8, MAGE A9, MAGE A 10, MAGE All, MAGE A 12 (The MAGE A family). Two other groups of proteins are also part of the MAGE family although more distantly related. These are the MAGE B and MAGE C group. The MAGE B family includes MAGE B1 (also known as MAGE Xp1, and DAM 10), MAGE B2 (also known as MAGE Xp2 and DAM 6) MAGE B3 and MAGE B4—the Mage C family currently includes MAGE C1 and MAGE C2. In general terms, a MAGE protein can be defined as containing a core sequence signature located towards the C-terminal end of the protein (for example with respect to MAGE A1 a 309 amino acid protein, the core signature corresponds to amino acid 195-279).
The consensus pattern of the core signature is thus described as follows wherein x represents any amino acid, lower case residues are conserved (conservative variants allowed) and upper case residues are perfectly conserved.
Core Sequence Signature
(SEQ ID NO: 16)LixvL(2x)I(3x)g(2x)apEExiWexl(2x)m(3-4x)Gxe(3- 4x)gxp(2x)llt(3x)VqexYLxYxqVPxsxP(2x)yeFLWGprA(2x) Et(3x)kv
Conservative substitutions are well known and are generally set up as the default scoring matrices in sequence alignment computer programs. These programs include PAM250 (Dayhoft M. O. et al., (1978), “A model of evolutionary changes in proteins”, In “Atlas of Protein sequence and structure” 5(3) M. O. Dayhoft (ed.), 345-352), National Biomedical Research Foundation, Washington, and Blosum 62 (Steven Henikoft and Jorja G. Henikoft (1992), “Amino acid substitution matricies from protein blocks”), Proc. Natl. Acad. Sci. USA 89 (Biochemistry): 10915-10919.
In general terms, substitution within the following groups are conservative substitutions, but substitutions between groups are considered non-conserved. The groups are:                i) Aspartate/asparagine/glutamate/glutamine        ii) Serine/threonine        iii) Lysine/arginine        iv) Phenylalanine/tyrosine/tryptophane        v) Leucine/isoleucine/valine/methionine        vi) Glycine/alanine        
In general and in the context of this invention, a MAGE protein will be approximately 50% identical in this core region with amino acids 195 to 279 of MAGE A1.
Several CTL epitopes have been identified on the MAGE-3 protein. One such epitope, MAGE-3.A1, is a nonapeptide sequence located between amino acids 168 and 176 of the MAGE-3 protein which constitutes an epitope specific for CTLs when presented in association with the MHC class I molecule HLA.A1. Recently two additional CTL epitopes have been identified on the peptide sequence of the MAGE-3 protein by their ability to mount a CTL response in a mixed culture of melanoma cells and autologous lymphocytes. These two epitopes have specific binding motifs for the HLA.A2 (Van der Bruggen, 1994) and HLA.B44 (Herman, 1996) alleles respectively.